This investigation represents an alternative approach to the development of synthetic, non-thrombogenic surfaces. The active and complex metabolic processes of the endothelial cell, the only known non-thrombogenic surface, mitigate against discovery of truly non-thrombogenic, synthetic materials. Alternatively, we seek to determine which elements of the hemostatic system are directly activated by contact with synthetic surfaces, and then to discover inhibitors that prevent activation of these elements. Previous work has shown that synthetic surfaces directly activate Factor XII of the contact pathway, platelets and possibly white cells. In this proposal, we will study three new inhibitors of the contact pathway: corn trypsin inhibitor, a specific inhibitor of Factor XIIa; Ala 357 Arg358 alpha-1-antitrypsin, a double mutant of alpha-1-antitrypsin and a selective inhibitor of kallikrein and Factor XIIa; and arginine-15-aprotinin, a selective inhibitor of kallikrein and Factor XIa. We will determine the ability of these inhibitors to inhibit the contact pathway during in vitro and in vivo (dog) extracorporeal circulation. We will also determine whether neurtrophils are directly activated by surface contact or via the classical or alternative complement pathways and will develop strategies to inhibit neutrophil activation during extracorporeal circulation. We will determine the changes that occur in platelet membrane ADP, adrenergic and thromboxane receptors during clinical cardiopulmonary bypass and study three new strategies to inhibit platelet adhesion to and activation by synthetic surfaces. We will study three new platelet inhibitors to the platelet fibrinogen binding receptor GPIIb/IIIa: trigramin, a natural snake peptide; and two synthetic peptides, RGDS and "Ruggieri" peptide. We will also study in vitro and in vivo the role of von Willebrand factor in platelet adhesion to synthetic surfaces and the use of degraded fibrinogen to precoat synthetic materials to prevent platelet adhesion. Lastly, by combining inhibitors to the contract pathway, platelets and if necessary neutrophils, we hope to achieve extracorporeal circulation in vitro and in vivo without heparin and thus provide a new method to control the thrombotic and bleeding complications of synthetic materials in contact with blood.